Excel Services 2010 - "Excel - Unable to process the request - Wait a few minutes and try performing this operation again"


Symptoms


When attempting to render an Excel workbook in the browser (Excel Services) the below error was thrown:

 "Excel

Unable to process the request.

Wait a few minutes and try performing this operation again"

Cause


ASP.NET Impersonation was Enabled.

Resolution


Disable the ASP.NET Impersonation at the Server level and "SharePoint Web Services" level.

Via: IIS > Authentication > ASP.NET Impersonation